Salters chemistry (OCR B)- Unit 4

Precise key revision notes on chemistry of materials (F334)

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A2 Chemistry revision-Chemistry of Materials
1. The d block-transition metals
Transition metal- a d block element that forms at least one ion with a partially filled
sub-shell of d electrons
Physical properties compared to s-block metals:
i. D-block metals are also good conductors of heat and electricity
ii. They are also denser and have higher melting and boiling points.
iii. They are hard and durable.
Variable oxidation states
i. Due to the differences between successive ionisation enthalpies in the 3d and 4s
sub-shells are relatively small
ii. In lower oxidation states, the elements exist as simple ions (e.g. Cu², Cr³, Fe²)
and are oxidising agents.
iii. In higher oxidation states, the elements exist as anions (e.g. CrO²¯, MnO¯) and
are reducing agents.
iv. The 3d5 configuration is more stable than the 3d6 configuration
Formation of coloured ions
i. Only occurs in ions that have a partially filled 3d sub-shell
ii. The ions absorb visible light
Formation of complexes
Transition metal compounds are able to form complexes because their 3d orbitals can
accommodate the electrons donated by the ligands
i. Complex- a metal atom or ion is surrounded by ligands
ii. Complex ion- a complex with an overall charge
iii. Ligands-molecules or anions with one or more lone pairs of electrons that form
dative covalent bonds with the central metal atom or ion.
iv. Coordination number- number of bonds between the central metal and the
ligands
Catalytic activity
Transition metals can act as both:
i. Heterogeneous catalyst-provide a surface onto which the reactants are
absorbed. The 3d and 4s electrons form weak interactions that keep the
molecules in place while bonds are broken and formed.
ii. Homogeneous catalyst-as transition metals are able to change from one
oxidation state to another during the reaction, before returning to their original
oxidation state.
2. Redox and redox titrations
Potassium manganate (VII) titrations
Used to find the concentrations of solutions containing iron (II) ions or hydrogen
peroxide.
i. Pipette a known volume of solution (i.e. containing Fe ² ions) into a conical flask
ii. Acidify this solution with dilute sulphuric acid
iii. Slowly add potassium manganate (VII) to the solution in the conical flask from a
burette, swirling gently, until a pale pink colour persists.

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Repeat the titration to obtain 3 concordant results
Iodine ­ thiosulfate titrations
Used to find the concentration of solutions of oxidising agents.
i. A known amount of oxidising agent reacts with excess acidified potassium iodide
solution.
ii. The iodine produced is then titrated against a standard solution of sodium
thiosulfate.
iii. Near the end point of the reaction, a few drops of starch solution are added,
giving an intense blue/black colour, which disappears at the end point.
3.…read more

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Barrier protection- (i.e. painting, oiling, greasing and using polymer coatings) prevents
oxygen and water coming into contact with iron and steel
Galvanising-covering steel with thin layer of protective zinc that oxidises. Stainless steel
contains chromium that oxidises, leaving a protective oxide layer.
Sacrificial protection-attaching blocks of a more reactive metal (i.e. zinc) to large iron
structures. An electrochemical cell is formed and the reactive metal corrodes
preferentially.
6.…read more

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Condensation polymerisation-monomers join together to give a polymer and a small
molecule (i.e. HCL or HO)
i. Polyesters- dicarboxylic acid + diol
ii. Polyamides- diamine + dicarboxylic acid
Structure of a typical polymer is a mixture of:
i. Crystalline regions -ordered
ii. Amorphous regions - random
Glassy state- the amorphous regions become `frozen' therefore restricting movement. If
polymer has to change shape it does so by breaking
Effect of temperature
If you heat up a glassy material:
i.…read more

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In amorphous regions the polymer chains do not pack closely together and the
intermolecular bonds are very weak, therefore polymer chains will slide over each other
easily thus making the polymer flexible.
10. Green chemistry and recycling
11. Effect of concentration on rate
Rate of reaction- measure of how fast the reactants are used up or how fast the
products are formed.…read more

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Reaction mechanisms
i. By studying rate equations and orders we can deduce a mechanism for a reaction
ii. The rate equation for a reaction tells us which particles are involved in the rate
determining step.
iii. The rate determining step is the slowest step in a multi-step reaction.
12. Optical isomerism
Stereoisomers- molecules that have the same molecular formula and also have their
atoms bonded in the same order, but these atoms are arranged differently in space.
There are two types of stereoisomers:
i.…read more

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At high concentrations of substrate, the rate equation is rate = k [E] because all
the active sites have become saturated.
Hence the reaction is zero order with respect to the substrate
Enzymes are used as catalysts in industry because:
i. They are specific
ii. Work at low temperatures ­ this saves energy
iii. Work well in aqueous environment ­ reduces need for organic solvents, which
are flammable and damaging to the environment.
iv.…read more

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